Abstract
Ageing infrastructure are a concern for many wastewater utilities. This is accentuated with the presence of hydrogen sulfide within the sewer headspace, known to induce concrete corrosion, toxicity and odours. Some industrial effluents contain significant sulfide concentrations, however most field studies in the literature refer to domestic networks, or lab/pilot scale sulfide abatement strategies for varied effluents. Hence, the objectives of this work are: (1) To obtain data regarding the evolution of sulfides in a full-scale industrial sewer system in Portugal, receiving wastewater from a number of tanneries; (2) model their fate within the system and (3) experimentally evaluate sulfide precipitation with iron salts. Field work evidenced heavily sulfide loaded effluents, exceeding by far literature values for sewer systems. Modelling was carried out based on the AeroSept+ model, specifically calibrated to this type of effluent. Results showed the model was capable of reproducing the overall levels of sulfide in wastewater and H2S in the sewer headspace, while allowing insights into industrial discharges, originating a set of proposed interventions for sulfide abatement. This may be carried out by iron salts addition, in a ratio of 2.75:1, at existing monitoring stations. This approach was fundamental for an affordable performance assessment, under considerable uncertainty.
Highlights
While related to the wastewater inflow occurring at the moment within the sewer pipe, several related to the wastewater inflow occurring at the moment within the sewer pipe, several wastewater inflow observed thatthat do not in an in increase in hydrogen sulfide (H2 S) in within wastewater inflowevents eventscan canbebe observed do translate not translate an increase the system
The recommend strategy is, the implementation of a PID controller, able to control dosage of iron chloride based on real-time measurements of sulfide at the monitoring stations, until it reaches desired levels at the WWTP inlet. This system may require additional calibration/tuning in situ once it is implemented, and more work is recommended for dosage optimisation in real time
An existing model (AeroSept+) was adapted and calibrated for use in simulating sulfide and H2 S contents in an industrial sewer system, receiving mostly industrial effluents from tanneries with high sulfide contents. Characterisation of such effluents in industrial sewer systems was found scarce in the literature, especially regarding concentration of sulfide and H2 S and its impacts
Summary
Ageing infrastructure are of growing concern for utilities and municipalities in many developed countries, where managers struggle with problems associated with operating and managing infrastructure installed decades ago [1,2]. These problems are accentuated with presence of hydrogen sulfide (H2 S) within the sewer headspace, known to induce infrastructure corrosion, generate toxic environments and severe odour nuisance [3,4]. Corrosion attack inside sewer systems (as opposed to the exterior pipe wall in contact with the soil), results mostly from those biological processes that take place in the unsubmerged biofilm attached to sewer walls [5,6]. That mechanism can be succinctly described as a sequence of three fundamental stages [7], starting with the abiotic process of carbonation, followed by H2 S acidification, and the biological generation of sulfuric acid (H2 SO4 ) in moist conditions, capable of reacting with concrete surfaces [8,9]
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